Heat developable paper



p 1964 M. F. BAUMANN ETAL 3,149,993

HEAT DEVELOPABLE PAPER Filed Jan. 30, 1963 CO-CRYSTAL ADDUCT OF AN AMINE AND A HYDROXYPHENYL SUBSTITUTED CHROMAN POLYVALENT METAL SALT ORGANIC SPOT TEST REAGENT IIIIII/IIIIIIIIIIIIIIIIII SUPPORT INVENTORS MICHAEL E BAU MANN BY WILLIAM R. LAWTON ATTORNEYS United States Patent 3,149,993 HEAT DEVELOPABLE PAPER Michael F. Baumann, Hudson, and William R. Lawton, Nashua, N.H., assignors to Nashua Corporation, Nashua, N.H., a corporation of Delaware Filed Jan. 30, 1963, Ser. No. 255,085 7 Claims. (Cl. 117-363) This invention relates to heat marking processes and provides a novel heat sensitive sheet useful for copying and recording uses, and characterized by the ability to form a mark of contrasting color when heated to an activation temperature in the range of 50-150" C. Sheets of this type are commonly employed in thermographic copying processes, in which a sheet is placed next to a graphic original and is exposed with the original to infrared radiation which causes selective heating of the dark areas of the original sufiicient to form a copy thereof on the copy sheet. A detailed description of this process is set forth in US. Patent No. 2,740,896. The sheets of this invention may also be used in recording devices in which marking is accomplished by means of a heated stylus.

The present application is a continuation-in-part of application Serial No. 167,180, filed January 18, 1962, now abandoned.

In the heat marking sheets of this invention, materials which are reactive to form a colored compound are incorporated in the sheet in intimate association. These materials, referred to herein as precursors of the colored compound, include an ionizable polyvalent metal salt, and an electron donor organic reagent which forms a distinctly colored covalent coordination metallo-organic complex with the metal ions of the salt. Typical of these are the salts of metals which may be identified by spot test techniques and reagents useful for spot tests, as well as salts and organic reagents which combine in other similar known color forming reactions with the formation of a colored covalent coordination metallo-organic complex.

In the heat marking sheets of this invention, both of the precursors are present as physically distinct but intimately associated components. A heat responsive reaction between these components is brought about by providing a solid stable co-crystal adduct in which the carrier compound is either a bisphenol or an hydroxyphenyl substituted chroman-and the included compound is a liquid organic ammonia derivative, e.g., organic amines or amides, hydrazine derivatives and guanadine derivatives, to name but a few. Solid adducts of this type are well known; many are described in U.S. Patent No. 2,829,175. The hydroxyphenyl substituted chromans are described by Cramer, "Einschlussverbindungen," Springer-Verlag, Berlin, 1954, and a number are set forth in detail in the application of William R. Lawton, Serial No. 206,186, filed June 29, 1962, assigned to the assignee of this application. The entire disclosure of the above application is incorporated herein by reference.

In the heat sensitive sheets of this invention, the cocrystal adduct dissociates when heated and thereupon releases its liquid organic ammonia derivative which then serves as the vehicle for the color forming reaction between the precursors of the colored compound. Presumably, color formation is due to the ability of the organic ammonia derivative to cause the metallic salt to ionize and thereby bring the metallic salt and organic reagent into reactive association. The ammonia derivatives do not appear to enter into any kind of chemical reaction with either of the other color-forming reagents, but on the contrary serve what is essentially a physical function.

The color body precursors should be lightly colored, solid, non-hydroscopic, and otherwise stable, at normal conditions of temperature and humidity, that is, those conditions one might expect to encounter in actual conditions of storage, shipment, and use. The co-crystal adduct should be similarly stable, and lightly colored, and should in addition he dissociable to yield the ammonia derivative at the desired activation temperature in the range of 50150 C. The particular bisphenol or hydroxyphenyl substituted chromans and ammonia derivatives are accordingly to be selected with reference to these criteria on the basis of known, or readily ascertainable, characteristics of materials of this type.

In typical representative embodiments of this invention, the metal salt, the organic reagent and the co-crystal adduct are dispersed separately or together in a binder solu tion and applied as one or more coatings to a paper or other base by conventional techniques. The relative proportions of the color compound precursors (metal salt and organic reagent) should be such as to provide mutual reaction, with a total concentration sufficient to produce a distinct contrasting color mark when the sheet is heated. The amount of co-crystal adduct should be sufficient to provide enough of the ammonia derivative as a reaction vehicle to bring about a color forming reaction between the color compound precursors. These quantities may be determined by routine experimentation. While the amount of organic ammonia derivative employed may vary considerably depending upon the particular color compound presursors selected it has been found that most effective results are obtained when the ammonia derivative is provided in an amount equal to at least about 5% of the weight of the precursors.

The following examples described in detail several representative embodiments of this invention.

Example I A co-crystal adduct is first formed by combining:

Grams Tetrachloro bisphenol A (TCBA) 183 Ethanol amine (EA) 61 Toluene 364 by dissolving the TCBA in the toluene at 150 F., adding the ethanol amine and stirring for 30 minutes. The mixture is chilled to about 30 F. and held at that temperature for about 14 hours (overnight) during which time a precipitate forms. This is filtered off, washed thoroughly with n-hexane at room temperature F.) and dried. The solid crystal product is the co-crystal adduct of tetrachloro bisphenol A and ethanol amine (TCBA/EA) having a melting point of 96104 C.

A dispersion is prepared of:

Grams TCBA/EA 10 Polyvinyl butyral (Butvar B-76) 2.5 Trichloro ethylene 87.5

The mixture is charged in a ball mill and milled overnight at 40 F.

A second dispersion is prepared consisting of Parts by Weight Dithiooxamide (rubeanic acid) H 2.5 Polyvinyl -butyral (Butvar 13-76) 2.5 Trichloroethylene 95 This mixture is similarly charged in a ball mill and milled over night at 40 F.

A third dispersionis prepared consisting of:

Parts by weight Nickel oxalate 10 Polyvinyl butyral (Butvar B-87) 2.5 Trichloroethylene 87 .5

This mixture is dispersed in the same manner as the dispersions prepared above.

A mixture of the three dispersions is prepared in the proportions of 3 parts of dispersion A, parts of dispersion B, and 2 parts of dispersion C. After thorough mixing, this is coated in the conventional manner upon a 25-pound per ream (500 sheets, 24 x 36") glassine base to a coating weight of 4 pounds per ream. The coated paper is dried in air and may be used in a recording machine having a heated stylus, e.q., a Viso-cardiette electrocardiograph, a trace velocity of 100-300 inches per second. The sheets may also be used in thermographic processes, e.g,, in a Minnesota Mining and Manufacturing Company Thermofax copier, Model 17H, at settings of from 1 to 5.

By Way of counter examples, it is pointed out that omitting dispersion A, and combining 5 parts of dispersion B and 2 parts of dispersion C, and coating this mixture in the same manner as in Example I does not provide a sheet that is susceptible to heat marking.

Example II A co-crystal adduet is formed according to the procedure of Example I from a combination of:

Grams Tetrachlorobisphenol A (TCBA) 183 Diethanolarnine (DEA) 5 Toluene 364 The solid crystal product is the co-crystal adduct TCBA/ DEA having a melting point of 151153 C.

A dispersion is prepared of:

Parts by weight TCBA/DEA 10 Ethyl hydroxy ethyl cellulose (EHEC) 2.5 .Hexane 86 Methyl alcohol 2 in a ball mill and milling overnight at 40 F.

A second dispersion is prepared consisting of:

Parts by weight Diphenylcarbazide 5 EHEC 2.5

Parts by weight n-Hexane 86 Ethyl alcohol 2 and milling the mixture in a ball mill at F. overnight.

A heat marking sheet is prepared by first coating a 5% solution of cadmium nitrate in a 40-60 by Weight methanol-Water mixture on a 25-pound per ream glassine sheet to a Wet thickness of about 1 mil. After the sheet has been dried, a 6% solution of gelatin in a 4060 by Weight methanol-Water mixture is applied to a coating thickness of 2 mils Wet. After the gelatin coating has dried, a mixture consisting of 2 parts of dispersion A and 1 part of dispersion B is applied to a dry weight of 5 pounds per ream. Upon drying a heat marking sheet suitable for copying and recording purposes is provided.

Example III A co-crystal adduct is formed according to the procedure of Example I from a combination of:

. Grams Tetrachlorobisphenol A (TCBA) 183 Dimethylformamide (DMF) 73 Toluene 364 The solid crystal product is the co-crystal adduct TCBA/ DMF having a melting point of 6065 C.

A dispersion is prepared of:

Grams TCBA/DMF 10 Vinyl toluene/butadiene resin (Pliolite VT) 2.5 VM & P Naphtha 87.5

The mixture is charged in a ball mill and milled Overnight at 40 F.

A second dispersion is prepared consisting of:

Grams Ferric sulfate 5 Pliolite VT 5 VM & P Naphtha 25 This mixture is charged in a ball mill and milled overnight at 40 F.

night at 40 F.

A heat marking sheet is prepared by first coating on a 25-pound per ream glassine sheet, to a coating weight of 5 pounds per ream, a mixture of equal parts of dispersion B and dispersion C. This coating When dried is topcoated with a 3 pound per ream coating from dispersion A. The resulting sheet provides an eifective heat marking copy or recording medium.

Numerous other polyvalent metal salts may also be utilized in the preparation of sheets according to the present invention, including nickel formate, cobalt oxalate, nickel sulfate, aluminum chloride, copper oxalate, lead chloride, zinc sulfate, manganese chloride, nickel tartrate, ferrous oxalate, barium chloride, and chelates of nickel chloride with such compounds as 1,3-propylenediamine, tetramethylenediamine, and diamine hexane.

Among the many organic reagents that form colored covalent coordination metallo-organie complexes with polyvalent metal ions and that are suitable for use in compositions of this invention are included dithiooxalic acid and its potassium salt, biuret, 8-hydroxyquinoline, benzoinoxime, 2,2'-dipyridyl, anthranilic acid, pyrogallol, alizarin, tannin, carminic acid, morin, 2,3-butane dioneoxime thiocarbazide.

In addition, the numerous combinations of metals and spot test reagents, such as those listed in US. Patent No. 2,663,656, and also in Fiegle, Qualitative Analysis by Spot Tests, may be used.

The hydroxyphenyl substituted chromans have been found to be especially useful carrier compounds. Their co-crystal adducts with organic ammonia derivatives are generally water-insensitive, have excellent storage stability, and usually possess dissociation temperatures in a range which is well suited to the thermographic process. Examples in which these compounds are the carriers follow.

Example IV 7,4-diethyl-2'-hydroxy-2,4,4 trimethyl flaven was prepared according to the procedure described by Baker, Mc- Omie, and Wild, J. Chem. Soc., 1957, 3060-4.

m-Ethylphenol (105 g.) dissolved in anhydrous acetone (43 g.) was saturated one hour with anhydrous HCl at 0 C. The solution was kept at room temperature for two days, then warmed to 40 C. for six hours and stirred into an aqueous 2 N. NaOH solution (500 cc.) to which 60 cc. diethyl ether was added. After two days at 20 C., the semi-solid product was collected in a Biichner funnel, dissolved in hexane, and treated with calcium chloride. After filtering, the dried hexane solution of 7,4-diethyl-2-hydroxy-2,4,4-trimethylflavan was treated with grams cyclohexylamine and chilled for 24 hours at 20 C. The precipitate was collected and yielded 38 g. of the cyclohexylamine/flavan complex as a fine, white microcrystalline product (M.P. 77-79 C.).

Example V Cyclohexanespiro-4-(2'-hydroxy-7,4'-dimethyl-2,3-tetramethylene) flavan was prepared according to the procedure described by Baker, McOmie, and Wild, J. Chem. Soc., 1957, 3060-4.

A mixture of m-cresol (400 g.) and cyclohexanone (240 g.) was saturated with dry HCl for one hour at 0 C., kept for three days at room temperature and one day at 40-50 C. and stirred into 4 liters of an aqueous 2 normal sodium hydroxide solution. The product was extracted with a mixture of 1000 cc. diethylether and 400 cc. hexane.

The resulting solution was washed with Water, dried over calcium chloride, and treated with charcoal, and was finally evaporated to dryness. The resinous cyclohexanespiro-4-(2.-hydroxy- 7,4'- dimethyl 2,3 tetramethylene) flavan was redissolved in hexane and aliquot portions were treated with benzylamine and cyclohexylarnine, the solutions were chilled for 48 hours at -20 F., the amine complexes were filtered off, washed with cold hexane, and dried (M.P. of benzylamine complex 1l6116.5 C., M.P. cyclohexylamine complex 111-l17 C.).

Example VI 2-hydroxy-2,4,4,6,7,4',5-heptamethylflavan was prepared by the procedure described by Baker, McOmie, and Wild, J. Chem. Soc., 1957, 3060-4.

H01 CHgOCHa CH3 0 OH \i I t CH CH3 0H3 CH3 CH3 A solution of 3,4-dimethyl phenol (370 g.) in acetone (15-0 g.) was saturated at room temperature for one hour with anhydrous hydrogen chloride, after which it set to a red crystalline mass. After three days the reaction mixture was crushed with an excess of dilute sodium hydroxide, washed, dried, and crystallized twice from isopropanol. (M.P. of the 2-hydroxy-2,4,4,6,7,4,5-heptamethylflavan was 161-162.5 C.).

The diethanolamine complex was prepared by treating 30 g. of the flavan in a hexane-toluol solution with 10 g. diethanolamine. A solid product was obtained after chilling overnight at -20 C. The yield of the diethanolamine/flavan complex was 32.5 g. and the melting point was 153-7" C. with considerable softening at much lower temperature.

Example VII 2'-hydroxy-2,4,4,6,5-pentamethylfiavan was prepared by the procedure described by Baker, Curtis, and McOmie in J. Chem. Soc., 1952, 1774-85.

p-cresol (647 g.) dissolved in acetone (232. g.) was cooled to 0 C. in an ice-salt bath and saturated for one hour with gaseous HCl. During this period, the temperature rose to 15 C. The flask was sealed from atmospheric moisture, allowed to reach room temperature slowly and stood at room temperature for two days. After two days, the dark product was stirred into two liters of aqueous two normal sodium hydroxide solution during which time the mixture became colorless. Dioxan (400 g.) was added and the mixture was stirred on the water bath for thirty minutes and left overnight at 20 C. The solid was collected and dried over calcium chloride under vacuum and recrystallized from 600 cc. of hexane with the addition of 20 g. dioxane to give the dioxane/2-hydroxy-Z,4,4,6,5-pentamethyl flavan (M.P. 66-77 C.).

Twenty grams of the flavan/dioxane complex, 10 g. amine were dissolved in cc. of warm hexane, placed in the cold-box at 20 C. for four hours, and the solid amine complexes were collected in a Biichner funnel and dimethyl acetamide.

. 7 Washed once with cold hexane. The following amines were complexed in this manner:

2-hydroxy-2,4,4,6,5 -pentamethylflavan/cyclohexamine,

M.P. 57-66 C.

2-hydroxy-2,4,4,6,5 -pentamethylflavan/dicyclohexylamine, M.P. 101-105 C.

2' -hydroxy-2,4,4,6,5 -pentamethylflavan/diethylamine,

M.P. 65-68 C.

2'-hydr0xy-2,4,4,6,5 -pentamethylflavan/diisopropylamine, M.P. 68-76 CC.

2'-hydroxy-2,4,4,6,5 '-pentamethylflavan /di-n-butylamine,

M.P. 60-63 C.

2'-hydroxy-2,4,4,6,5 '-pentamethylfiavan/diamylamine,

M.P. 67-70 C.

2'-hydr0xy-2,4,4,6,5 '-pentamethy1fiavan/di-Z-ethylhexylamine, M.P. 66-69 C.

Example VIII 2-hydroxy-2,4,4,7,4'-pentamethylflavan was prepared by the procedure described by Baker and Besley in J. Chem. Soc., 1951, 1103-6.

HCl 011 0011;

OH OH i /O\(l3H3 4 H zdays O CH3 CH3 A mixture of m-cresol (440 g.) and acetone (260 g.) was saturated with gaseous HCl without cooling, and kept at 40 C. for two days with the exclusion of water. The dark product was added to an excess of an aqueous 20% sodium hydroxide solution, a layer of ether poured on the surface, and the mixture was vigorously stirred, causing the ether addition product of the dimeride to crystallize. After standing overnight in an open vessel, the solid was collected, Washed thoroughly with water, dissolved in hexane, and dried over calcium chloride. To the filtered solution was added a little ether. The ether adduct separated in large, colorless, thick rhombic prisms, M.P. 76-77 C. Fifteen grams of the ether complex in 150 cc. hexane was treated with amine, chilled overnight, and filtered to give complexes with 7 /2 g. of the following amines: 2'-hydroxy-2,4,4,7,4-pentamethylflavan/benzylamine,

M.P. 88-91 C. 2'-hydroxy-2,4,4,7,4-pentamethylflavan/cyclohexylamine,

M.P. 70-73 C. 2-hydroxy-2,4,4,7,4'-pentan1ethylfiavan/dicyclohexylamine, M.P. l03-105 C. 2'-hydroxy-2,4,4,7,4-pentamethylfiavan/morpholine +H O, M.P. 94-96 C. 2-hydroxy-2,4,4,7,4-pentamethylflavan/diethylamine,

M.P. 72-78 C. 2-hydroxy-2,4,4,7,4-pentamethylfiavan/diisopropylamine, M.P. 83-87 C.

Other organic ammonia derivatives representative of those that might be employed in the foregoing illustrative and suggested compositions include tetramethyl guanadine, ethyl ethanol amine, phenyl ethanol amine, dibutylamine, hydrazine N-Z-hydroxyethyl 1 methyl dodecylamine, formamide, piperidine, triethanolamine, cyclohexylamine, Numerous other bisphenols may be used in the formation of the co-crystal adducts of the organic ammonia derivatives, including tetrabromobisphenol A, bithionol, bisphenol A as well as others listed in the above-identified Patent No. 2,829,175.

The hydroxyphenyl substituted chroman/amine complexes may be incorporated into the'color-forming, heatreactive coatings in the same manner as has been described in connection with the bisphenol/ amine adducts, i.e., all three dispersions in organic liquids may be combined into a single coating composition. However, because of the greater stability of the chroman/ amine complexes as contrasted with the bisphenol/amine adducts, they may also be applied from aqueous solutions of binders which can be water-soluble polymers such as glue, starch, polyvinyl alcohol, Water-soluble gums, carboxymethyl cellulose, hydroxyethyl cellulose and like substances. These binders are less compatible with the chroman/ amine adducts than are the organic solvent-soluble types and therefore have less tendency to interact with the adduct. This fact contributes to the storage stability of the chroman/ amine systems.

When water-soluble binders are used, the general coating procedure is as follows.

A ball-mill grind is made containing:

Parts by weight Water 98 Polyvinyl alcohol 2 The chroman/ amine complex 20 The mixture is ball-milled at 24-48 hours and then coated on the sheet material by conventional coating machinery.

Test coatings were coated with a No. 12 Mayer rod on 45-lb. stock to give a weight-coat of 3-5 lbs. per ream of 24" x 36" x 500 sheets.

The dried amine complex coatings were overcoated with the various color-forming systems to give a top coat dry Weight of 0.5-2 lbs. per ream.

Example IX A. 20 parts of 7,4'-diethyl-2'-hydroxy-2,4,4-trimethyl flavan (Example IV) was 'grounded in a ball-mill for 24 hours in a 2% water solution of polyvinyl alcohol.

B. SuspensionA was coated on 25 lbs. glassine base (24 x 36" x 500 pages) to a coating weight of 4 lbs. per

ream.

C. 5 parts of nickel oxalate, 2.5 parts of dithiooxamide (rubeanic acid), 2.5 parts of polyvinyl butyral (Butvar B-76), 87.5 parts of trichloroethylene was grounded in a ball mill for 24 hours.

Suspension C was overcoated on the dried coated sheet (B) to a coating weight of 2 lbs. per ream.

The coated sheet Will give clear, colored indicia under a heated stylus or in a thermographic copy machine.

The following hydroxyphenyl substituted chroman/ amine co-crystalline adducts Were substituted for the 7,4- diethyl-2-hydroxy-2,4,4-trimethyl flavan/cyclohexylamine adduct and, save for differences in the decomposition temperature of the adduct, were found to give substantially equivalent results.

2-hydroxy-2,4,4,7,4'-pentamethylflavan/diethylamine 2-hydroxy-2,4,4,7,4-pentamethylflavan/diisopropylamine 2'-hydroxy-2,4,4,7,4'-pentamethylflavan/benzylamine 2-hydroxy-2,4,4,7,4-pentamethylflavan/cyclohexylamine 2'-hydroxy-2,4,4,7,4-pentan1ethylflavan/dicyclohexylamine Cyclohexanespiro-4- (2-hydroxy-7-4-dimethyl-2,3 -tetramethylene) flav an/benzylamine Cyclohexanespiro-4- (2-hydroxy-7,4'-dimethyl-2,3-tetramethylene) flavan/cyclohexylamine 2-hydroxy-2,4,4,7,4'-pentamethylflavan/morpholine 2'-hydroxy-2,4,4,6,7,4',5 -heptamethylflavan/diethanolamine 4-p-hydroxyphenyl-2,2,4-trimethylchroman Dianins Compound) /diethylamine 2-hydroxy-2,4,4,6,5 -pentamethylflavan/cyclohexylamine 2'-hydroxy-2,4,4,6,5-pentamethylflavan/diethylamine 2-hydroxy-2,4,4,6,5 '-pentarnethylflavan/di-n-butylamine 2-hydroxy-2,4,4,6,5-pentamethylfiavan/diisopropylamine 2'-hydroxy-2,4,4,6,S -pentamethylflavan/diamylamine 2-hydroxy-2,4,4,6,5 '-pentamethylflavan/di-2-ethylhexylamine 2'-hydroxy-2,4,4,6,5'-pentarnethylfiavan/dicyclohexylamine All of the foregoing coating compositions may be applied to sheets or webs by conventional paper coating machinery.

The variety of acceptable methods and procedures for applying the coating compositions of the present invention is illustrated in foregoing representative examples. The coating techniques specifically employed in these examples may be interchanged without loss of response upon activation of the resulting sheets.

Co-crystal adducts suitable for a particular application should be selected with reference to the dissociation temperature, which may be determined by mixing the adduct with a mixture of nicket oxalate and rubeanic acid in the dry state and heating slowly until a color is formed. The co-crystal adduct should also be selected with reference to its stability, color, and hydroscopic properties, so as to impart the desired properties in the paper.

The sheets described in the foregoing examples have activation temperatures of a range of 50-150 C., as determined by placing the sheet on a heated surface for 1 second, and measuring the lowest temperature at which a visibly distinct color change occurs in the heated area.

The accompanying drawing illustrates schematically a heat sensitive sheet corresponding to this invention. The sheet is represented as being in cross section.

Although this invention has been described with reference to representative and preferred embodiments, it is contemplated that obvious modifications will occur to those skilled in the art and familiar with these teachings, and that such may be made without departing from the scope of this invention. Other color forming systems based on ionizable polyvalent metal salts and organic reagents capable of forming covalent coordination complexes having a distinct coloration with such metals are known in the art and many of them will undoubtedly be found to be useful in this invention. Other carrier compounds and organic ammonia derivations may also be employed, provided that selection is made on the basis of the criteria set forth herein. Other ingredients may also be included in the coating such as anti-tack agents, anti-fingerprinting agents, anti-static agents, fillers, and coloring compounds, and bases other than glassine, e.g., regenerated cellulose, cellulose esters, other forms of paper and plastic materials may also be used if desired.

This application is a continuation in part of applicants co-pending application Serial No. 167,180, filed January 18, 1962.

Having thus disclosed our invention and described in detail preferred embodiments thereof, we claim and desire to secure by Letters Patent:

1. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C.-150 C. by changing visibly and irreversibly to a contrasting color through the formation of a colored compound, said sheet including a solid stable ionizable polyvalent metal salt and a solid stable organic reagent reactive with the metal ions of said salt in the presence of a liquid ammonia derivative to form a colored metallo-organic compound by covalent coordinate bonding between said metal ions and said reagent, said salt and reagent being precursors of said colored compound present in said sheet in physically distinct potentially reactive association, and a solid, stable crystalline cocrystal adduct of a liquid organic ammonia derivative and a hydroxyphenol carrier compound selected from the class consisting of bisphenols and hydroxyphenyl substituted chromans, said adduct having a dissociation temperature of between 50 C. and 150 C. at which temperature said '1'0 liquid ammonia derivative is released by said carrier compound, causing said salt and reagent to react.

2. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions responsive to heating to an activation temperature in the range of 50 C. C. by changing visibly and irreversibly to a contrasting color through the formation of a colored compound, said sheet including solid stable precursors of said compound in physically distinct intimate potentially reactive association, one of said precursors being an ionizable polyvalent metal salt and the other being an organic reagent reactive with the metal ions from said salt in the presence of a liquid ammonia derivative to form a colored metallo-organic compound by covalent coordinate bonding between said metal ions and said reagents, and a solid stable crystalline co-crystal adduct of a liquid organic ammonia derivative and a hydroxyphenol carrier compound selected from the class consisting of bisphenols and hydroxyphenyl substituted chromans, said adduct dissociating at a temperature of from 50 C.150 C. to yield said ammonia derivative and thereby provide a vehicle for the color-forming reaction between said salt and said reagent.

3. A heat sensitive sheet as claimed in claim 1 wherein said solid, stable, ionizable metal salt is nickel oxalate, and said organic reagent is rubeanic acid.

4. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C.150 C. by changing visibly and irreversibly to a contrasting color through the formation of a colored compound, said sheet comprising a web of flexible sheet material, and a layer coated thereon and adherent thereto and comprising an intimate and uni form potentially reactive mixture of a solid stable ionizable polyvalent metal salt, a solid stable organic reagent reactive with the metal ions of said salt in the presence of a liquid ammonia derivative to form a colored metalloorganic compound by covalent coordinate bonding between said metal ions and said reagent, and a solid, stable crystalline co-crystal adduct of a liquid organic ammonia derivative and a hydroxyphenol carrier compound selected from the class consisting of bisphenols and hydroxyphenyl substituted chromans, said adduct: having a dissociation temperature of between 50 C. and 150 C. at which temperature said liquid ammonia derivative is released by said carrier compound, thereby providing a medium for the color-forming reaction between said salt and said reagent.

5. A heat sensitive sheet adapted for dry heat marking processes, stable and lightly colored under normal conditions and responsive to heating to an activation temperature in the range of 50 C.-150 C. by changing visibly and irreversibly to a contrasting color through the formation of a colored compound, said sheet comprising a web of flexible sheet material, and a layer coated thereon and adherent thereto and comprising, in physically distinct potentially reactive association, a solid stable ionizable polyvalent metal salt, a solid stable organic reagent reactive with the metal ions of said salt in the presence of a liquid ammonia derivative to form a colored metallo-organic compound by covalent coordinate bonding between said metal ions and said reagent, said salt and said reagent being precursors of said colored compound, and a solid stable crystalline co-crystal adduct of a liquid organic ammonia derivative and a hydroxyphenol carrier compound selected from the class consisting of bisphenols and hydroxyphenyl substituted chromans, said adduct having a dissociation temperature of between 50 C. and 150 C. at which temperature said liquid ammonia derivative is released by said carrier compound, thereby providing a medium for the color-forming reaction between said salt and said reagent.

6. A heat sensitive sheet as claimed in claim 5 wherein said layer further comprises a plurality of distinct super- 1 1 1 2 posed coatings, one of said coatings comprising finely di- References Cited in the file of this patent vided particles of said co-crystal adduct uniformly dis- UNITED STATES PATENTS tributed in an adhesive binder.

7. A heat sensitive sheet as claimed in claim 6 wherein 2,663,656 M11181: et a1 1953 said co-crystal adduct comprises an adduct of a liquid 5 2,899,334 Crevhng et a1 11, 1959 organic ammonia derivative and a hydroxyphenol substi- 2,967,785 Allen at 1961 tuted chroman, and said adhesive binder comprises a 2,995,466 Sorensen 1961 Water-soluble, organic solvent-insoluble film-forming pol- 3,024,362 et a1 6, 1962 3,076,707 Lawton et a1 Feb. 5, 1963 ymer, and wherein another of said plurality of coatings comprises a uniform distribution of said precursors in an 10 organic solvent-soluble film forming polymer binder.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 149,993 September 22 196 Michael F. Baumann et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 43, for "described read describe column 3, line 37, for "e.q." read e.g. line 38, before "a trace" insert at column 5, line 19, for "flaven" read flavan column '7, line 3, for "cyclohexamine" read cyclohexylamine column 8 line 24 strike out "at"; line 36, for "grounded" read ground line 43, for "was grounded" read were ground line 62, for "74 read 7 ,4 line 70, for "Dianin' 5" read (Dianin's column 9, line 18, for "nicket" read nickel line 42, for "derivations" read derivatives Signed and sealed this 12th day of January 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patem 

1. A HEAT SENSITIVE SHEET ADAPTED FOR DRY HEAT MARKING PROCESSES, STABLE AND LIGHTLY COLORED UNDER NORMAL CONDITIONS AND RESPONSIVE TO HEATING TO AN ACTIVATION TEMPERATURE IN THE RANGE OF 50*C.-150*C. BY CHANGING VISIBLY AND IRREVERSIBLY TO A CONTRASTING COLOR THROUGH THE FORMATION OF A COLORED COMPOUND, SAID SHEET INCLUDING A SOLID STABLE IONIZABLE POLYVALENT METAL SALT AND A SOLID STABLE ORGANIC REAGENT REACTIVE WITH THE METAL IONS OF SAID SALT IN THE PRESENCE OF A LIQUID AMMONIA DEREVATIVE TO FORM A COLORED METALO-ORGANIC COMPOUND BY COVALENT COORDINATE BONDING BETWEEN SAID METAL IONS AND SAID REAGENT, SAID SALT AND REAGENT BEING PRECURSORS OF SAID COLORED COMPOUND PRESENT IN SAID SHEET IN PHYSICALLY DISTINCT POTENITALLY REACTIVE ASSOCIATION, AND A SOLID, STABLE CRYSTALLINE COCRYSTAL ADDUCT OF A LIQUID ORGANIC AMMONIA DERIVATIVE AND A HYDROXYPHENOL CARRIER COMPOUND SELECTED FROM THE CLASS CONSISTING OF BISPHENOLS AND HYDROXYPHENYL SUBSTITUTED CHROMANS, SAID ADDUCT HAVING A DISSOCIATION TEMPERATURE OF BETWEEN 50*C. AND 150*C. AT WHICH TEMPERATURE SAID LIQUID AMMONIA DERIVATIVE IS RELEASED BY SAID CARRIER COMPOUND, CAUSING SAID SALT AND REAGENT TO REACT. 